 |
|
 |
|
|
North American Multi-Model Ensemble Teleconference Strong relations between ENSO and the Arctic Oscillation in the NMME |
|
|
September 6, 2018 Discussions continued on the hot topic of the 2015-16 El Niño event and the prediction of California rainfall. The Arctic Oscillation (AO) impact is critical to improving middle- to high-latitude climate outlooks, and most models did not catch the positive AO observed during that season. Michelle L’Heureux, Lead of the El Niño-Southern Oscillation (ENSO) team, NOAA’s Climate Prediction Center did a more careful study, looking inside the complex problem. She demonstrated a strong correlation (r~0.9) between ensemble mean AO and ENSO values out to long lead times of 12 months in the NMME products, much stronger than the correlation in observations (Fig. 1). |
|
|
Though her studies revealed the NMME has some skill in predicting the AO out to 5-7 seasons for winter and early spring, she noted that not all the AO skill (forecast vs. observations) can be attributed to ENSO, especially at short lead times. While ENSO can impact the winter AO/NAO, the predictable signal was smaller than the unpredictable noise, suggesting the NMME is overdoing the AO-ENSO relationship, especially during the spring and fall. This sensitivity may arise from the models underrepresenting or missing other sources of predictability. The details were explored in her paper with coauthors (L’Heureux et al. 2017). Reference L’Heureux, M. L., M. K. Tippett, A. Kumar, A. H. Butler, L. M. Ciasto, Q. Ding, , K. J. Harnos, and N. C. Johnson, 2017: Strong relations between ENSO and the Arctic Oscillation in the North American Multimodel Ensemble. Geophys. Res. Lett., 44, 11,654–11,662. |
Fig. 1 Anomaly correlation between of the NMME ensemble mean Niño-3.4 and AO index values. Dots indicate the 5% significance level. The bottom row (Obs) indicates the contemporaneous correlation between the Niño-3.4 index and the AO index. The AO index has been inverted. The lead time is by month, for sliding seasonal averages. (From L’Heureux et al. 2017) |
|
Climate Prediction Center Drought Outlook Support Briefing Scientific highlights September 18, 2018 Climate Prediction Center (CPC) Drought Outlook Support Briefing presents the current hydro-climate conditions, objective drought assessment over the United States for the recent weeks, calendar month and three month season, supporting the operational National Drought Monitor and National Drought Outlook. This month’s drought briefing led by Dr. Muthuvel Chelliah examined current drought conditions and brought attention to the need for carefully monitoring the details of rainfall deficits and soil moisture conditions on time scales ranging from weeks to years across the continental United States. He also stressed the fact that our ability to predict future drought conditions, critically depends our ability to predict precipitation in the upcoming month and seasonal time scale by our operational forecast models. Drought outlook is based on its predictability that comes largely from 1) teleconnections induced by large-scale remote forcing, which SST anomalies dominate, and 2) local land surface characteristics, e.g. soil moisture, vegetation, snow cover etc., which impact either directly on the water and energy balance or through their memory effect on atmospheric variability and land surface hydrology. The challenges are the unpredictable internal atmospheric variability, such as development of synoptic systems that may also interact with drought regionally. The Briefing showed ENSO neutral conditions were currently present and under El Niño Watch with ~50-55 % chance of El Niño in the Northern Hemisphere fall 2018 and increasing to ~65-70% during winter 2018-19. Monitoring of regional drought condition indicated the Northern Plains drought, which was continuing from 2017, got improved in early/middle summer, but did not completely recover from May-September rains of this year. The predominant South/Southwest drought, a consequence of the rainfall deficit associated with two recent back to back La Niñas, was undergoing changes. Short term drought improvement/removal had been noted across parts of Kansas/ Oklahoma/ Missouri/ Arkansas/ Louisiana since last month. Dryness/Drought was expanding/developing in the Pacific Northwest states expanding into Idaho. Despite marginal chance of El Niño development in fall 2018, subsurface Pacific conditions were still shown reasonably warm and pointing towards El Nino. Accordingly, models and forecasters continued to predict/expect El Nino conditions to develop in Fall and Winter. In the next three months, all models indicated slightly above normal rainfall particularly across the South and West, dryness in the Pacific Northwest. |
|
|
The Program for the Oral and Poster Sessions are available online at NOAA/CPC website. Online registration to the Workshop is open and the details of registration, hotel and other information can be found at the website of the Meeting's local host organizer, Earth Research Institute and Department of Geography at the University of California Santa Barbara. |
"But in the upcoming season, seasonal rains will arrive especially in mid/late November and December all along Pacific western states and adjoining states. Increasing chances of El Nino will help the drought in the south and west, and hence contribute to improving short term improvement, but longer term dryness will persist. Much of the easten half of the United States will likely remain drought free", Dr. Chelliah added. |
